YouTube, the popular online video site, has begun removing more than 100,000 unauthorized clips belonging to Viacom -- everything from snippets of Jon Stewart's "The Daily Show" to Nickelodeon's "SpongeBob SquarePants."

The purge comes after Viacom demanded that YouTube take down the material, accusing the site of violating its copyrights. Viacom says it's the largest order to delete videos it has ever made.

The dispute reflects how popular San Bruno's YouTube has become as an online source of entertainment. And it highlights the dilemmas media companies face as they try to keep control of their material in the digital age.

Since exploding onto the Web less than two years ago, YouTube has drawn ire -- as well as millions of loyal fans -- for its vast and rapidly growing library of videos, many of them copyrighted clips from popular television shows and movies. The site's mushrooming popularity got the attention of Internet powerhouse Google, which bought YouTube for $1.65 billion last year.

Viacom, whose properties include MTV, Comedy Central, BET, TV Land and Nickelodeon, said it spent months negotiating with YouTube so that it could be paid for its material to appear on the site. That copyrighted material -- amounting to 1.2 billion streams, according to Viacom -- is uploaded by YouTube users, despite measures the site takes to stop the practice.

"YouTube and Google retain all of the revenue generated from this practice, without extending fair compensation to the people who have expended all of the effort and cost to create it," Viacom said in a statement.

YouTube said it takes copyright issues seriously, but it added that media companies gain from having their shows displayed.

"It's unfortunate that Viacom will no longer be able to benefit from YouTube's passionate audience, which has helped to promote many of Viacom's shows," a YouTube spokesperson said in a statement.

But in an interview, Viacom general counsel Mike Fricklas said that Viacom should have control over how and what it promotes. "When everyone gets a free pass to the movies, it's no longer promotional," he said.

YouTube has already struck partnerships with CBS, NBC and others to post authorized clips on the site. Last fall, CBS said that in the first month it operated a YouTube channel, it garnered 29.2 million views, and credited the partnership for increasing ratings.

By law, YouTube must take down copyrighted material when it is alerted to it. This happens regularly. Last fall, the Japanese Society for Rights of Authors, Composers and Publishers demanded that YouTube delete 30,000 copyrighted clips from the site.

Even NBC, which, like CBS, has a branded YouTube channel, continues to order YouTube to remove some 1,000 clips a month.

James McQuivey, principal analyst with Forrester Research, said he expects the two sides to return to the bargaining table quickly. By demanding its clips be erased from YouTube, Viacom is making a point that its shows offer more value than YouTube's other partners. Viacom shows appear on paid cable rather than broadcast channels, for instance, and "The Daily Show" and "The Colbert Report" are consistently on YouTube's top-watched lists.

On the other hand, YouTube and Google want to come to an agreement quickly because they don't want it to appear that media companies can play hardball and dictate deal terms, McQuivey said.